To complete the analysis, we consider the massive case, and the generic mass term that can be added to the invariant action is [1]}, [2]}, [3]}
\(S_m &=& \int d^4p\; \left(\frac{m_1}{4}\tilde{A}^{\mu \nu }\tilde{A}_{\mu \nu } + \frac{m_2}{8}\tilde{A}^2\right) \nonumber \\&=& \int d^4p\; \frac{1}{2} \tilde{A}_{\mu \nu }(m_1 \mathcal {I}^{\mu \nu , \rho \sigma } + m_2 E^{\mu \nu ,\rho \sigma })\tilde{A}_{\rho \sigma }\ ,\) 
